Transducers for measuring the torque in rotating axles are designed according to different principles. In some transducers the twist of the axle is measured over a certain axial length as the phase difference between the signals from two gear rings. In other transducers, the shearing stress in the axle is measured by different methods, for example by means of strain gauges, whereby the strain gauge and the signal processing circuit, mounted on the axle, are supplied via a rotating transformer and where the measuring signal is transmitted in a wireless manner.
In still other transducers, the shearing stress is measured by magnetoelastic methods, such as, e.g., in Swedish Pat. No. 167 387, in which the magnetic anisotrophy in the axle, caused by the shearing stress, is measured with the aid of a system of magnetizing and sensing magnetic poles arranged around the axle.
In a magnetoelastic transducer according to U.S. Pat. No. 4,506,554, a measuring axle is provided with a measuring sleeve which, in two separate zones, has been formed with slots which in one zone has a +45.degree. deviation from the axial direction and in the other zone a -45.degree. deviation from the axial direction. The difference in reluctance between the two zones, arising when applying a torque, is sensed by a surrounding coil system.
In all of the above-mentioned transducers, the wishes concerning the choice of stress level in the measuring axle at the upper limit of the measurement range are contradictory. To obtain a good signal/noise ratio and a small temperature dependence, a high maximum measuring stress should be chosen, but to obtain a good overload capacity without the zero point of the signal being changed, a low maximum measuring stress must be chosen, and therefore the signal/noise ratio and the temperature dependence are necessarily deteriorated.